Cassel played sparingly the past two seasons in Tennessee. The 13-year veteran has also played for Dallas, Buffalo, Minnesota, Kansas City and New England.

He started 15 games in 2008 with the Patriots when Lions general manager Bob Quinn and coach Matt Patricia also worked for the franchise. Cassel has started 81 games in his career, completing 59 percent of his passes for 17,449 yards with 104 touchdowns and 81 interceptions.

Jake Rudock, drafted by Detroit in the sixth round two years ago, and Cassel are expecting to compete to be Stafford's backup.